import {countColumn} from "./misc.js"

// STRING STREAM

// Fed to the mode parsers, provides helper functions to make
// parsers more succinct.

class StringStream {
    constructor(string, tabSize, lineOracle) {
        this.pos = this.start = 0
        this.string = string
        this.tabSize = tabSize || 8
        this.lastColumnPos = this.lastColumnValue = 0
        this.lineStart = 0
        this.lineOracle = lineOracle
    }

    eol() {
        return this.pos >= this.string.length
    }

    sol() {
        return this.pos == this.lineStart
    }

    peek() {
        return this.string.charAt(this.pos) || undefined
    }

    next() {
        if (this.pos < this.string.length)
            return this.string.charAt(this.pos++)
    }

    eat(match) {
        let ch = this.string.charAt(this.pos)
        let ok
        if (typeof match == "string") ok = ch == match
        else ok = ch && (match.test ? match.test(ch) : match(ch))
        if (ok) {
            ++this.pos;
            return ch
        }
    }

    eatWhile(match) {
        let start = this.pos
        while (this.eat(match)) {
        }
        return this.pos > start
    }

    eatSpace() {
        let start = this.pos
        while (/[\s\u00a0]/.test(this.string.charAt(this.pos))) ++this.pos
        return this.pos > start
    }

    skipToEnd() {
        this.pos = this.string.length
    }

    skipTo(ch) {
        let found = this.string.indexOf(ch, this.pos)
        if (found > -1) {
            this.pos = found;
            return true
        }
    }

    backUp(n) {
        this.pos -= n
    }

    column() {
        if (this.lastColumnPos < this.start) {
            this.lastColumnValue = countColumn(this.string, this.start, this.tabSize, this.lastColumnPos, this.lastColumnValue)
            this.lastColumnPos = this.start
        }
        return this.lastColumnValue - (this.lineStart ? countColumn(this.string, this.lineStart, this.tabSize) : 0)
    }

    indentation() {
        return countColumn(this.string, null, this.tabSize) -
            (this.lineStart ? countColumn(this.string, this.lineStart, this.tabSize) : 0)
    }

    match(pattern, consume, caseInsensitive) {
        if (typeof pattern == "string") {
            let cased = str => caseInsensitive ? str.toLowerCase() : str
            let substr = this.string.substr(this.pos, pattern.length)
            if (cased(substr) == cased(pattern)) {
                if (consume !== false) this.pos += pattern.length
                return true
            }
        } else {
            let match = this.string.slice(this.pos).match(pattern)
            if (match && match.index > 0) return null
            if (match && consume !== false) this.pos += match[0].length
            return match
        }
    }

    current() {
        return this.string.slice(this.start, this.pos)
    }

    hideFirstChars(n, inner) {
        this.lineStart += n
        try {
            return inner()
        } finally {
            this.lineStart -= n
        }
    }

    lookAhead(n) {
        let oracle = this.lineOracle
        return oracle && oracle.lookAhead(n)
    }

    baseToken() {
        let oracle = this.lineOracle
        return oracle && oracle.baseToken(this.pos)
    }
}

export default StringStream
